Compact PCI specifies a max of 8 slots (one of which is typically the system board). Regular PCI doesn't have a hard and fast slot limit (except for the logical limit of 32 devices per bus); the limits are driven by electrical loading concerns. As I recall, a bus of typical length can accommodate 10 "loads", where a load is either a device pin or a slot connector (that is, an expansion card counts as two loads, one for the device and one for the connector). (I take this to be a rule of thumb, not a hard spec, based on the detailed electrical requirements in the PCI spec.)

Still, the presence of bridges opens up the number of devices on a root PCI bus to a very high number, logically. Certainly having three or four quad Ethernet cards, so 12 or 16 devices, is a plausible configuration. As for bandwidth, a 64x66 PCI bus has a nominal burst bandwidth of 533 MB/second, which would be saturated by 20 full duplex 100baseT ports that were themselves saturated in both directions (all ignoring overhead). Full saturation is not reasonable for either PCI or Ethernet; I'm just looking at order-of-magnitude numbers here.

The bottom line is: don't make any hard and fast assumption about the number of devices connected to a root PCI bus.-- /Jonathan Lundell.-To unsubscribe from this list: send the line "unsubscribe linux-kernel" inthe body of a message to majordomo@vger.kernel.orgMore majordomo info at http://vger.kernel.org/majordomo-info.htmlPlease read the FAQ at http://www.tux.org/lkml/